Process for producing brilliant acrylic fibers of a noncircular crosssection

ABSTRACT

RELATES TO MAKING BRILLIANT NON-ROUND ACRYONITRILE POLYMER FIBERS HAVING SMOOTH SURFACES BY WET-SPINNING AN INORGANIC SOLVENT SOLUTION OF A POLYMER OF AT LEAST 85% ACRYLONITRILE CONTAINING 5-15% OF A DI(LOWER ALKYL) ACRYLAMIDE OR A DI(LOWER ALKYL) METHACRYLAMIDE. PREFERABLY, THE WET GEL FIBER SO PRODUCED IS TREATED WITH ACETONE AFTER WATER WASHING AND PRIOR TO STRETCHING.

United States Patent Ofice 3,767,755 Patented Oct. 23, 1973 US. Cl. 264-177 F 12 Claims ABSTRACT OF THE DISCLOSURE Relates to making brilliant non-round acryonitrile polymer fibers having smooth surfaces by wet-spinning an inorganic solvent solution of a polymer of at least 85% acrylonitrile containing 545% of a di(lower alkyl)acrylamide or a di(lower alkyl)methacrylarnide. Preferably, the wet gel fiber so produced is treated with acetone after water washing and prior to stretching.

This invention relates to a process for producing brilliant acrylic fibers of noncircular cross section. More particularly, this invention relates to a process for producing acrylic fibers of noncircular cross section wherein an inorganic solvent solution of an acrylonitrile polymer having a copolymerized content of a di(lower alkyl)acrylamide or corresponding methacrylamide is spun into a cogulant and then processed conventionally.

This application is a continuation-in-part application of US. application Ser. No. 180,904 filed Sept. 15, 1971, now abandoned.

It is well known that acrylic fibers of round cross section can readily be obtained by wet spinning an acrylonitrile polymer dissolved in an organic solvent through round orifices. It is also known that wet spinning of an aerylonitrile polymer through noncircular orifices can lead to acrylic fibers of noncircular cross section. However, when noncircular orifices are employed, it is necessary to maintain a very limited range of spinning conditions if fibers of noncircular cross section are to be obtained. Extension of the range of spinning conditions leads to fibers of round cross section.

Fibers of noncircular cross section have a variety of uses wherein their special characteristics are highly desira-ble. Particularly desirable are those fibers of noncircular cross -section which exhibit spectacular brilliance and luster when irradiated with sunlight or artificial light such as incandescent or fluorescent lamps. Such fibers are herein after referred to as brilliant fibers.

All fibers possessing noncircular cross section do not qualify as brilliant fibers. In order to qualify, it is necessary for the fibers to possess a surface that is smooth. The surface referred to is perpendicular to the fiber cross section and extends continuously at the outer periphery of the cross section in the longitudinal direction of the fiber. This requirement for smoothness is sometimes referred to as the fixed form factor.

The fixed fiber form factor is so likely to be influenced by the slightest variation in spinning conditions in accordance with conventional procedures for fibers of noncircular cross section that very strict control must be maintained. Such control is extremely difficult to effect.

In accordance with the present invention there is provided a process for producing brilliant acrylic fibers of noncircular cross section which comprises (1) preparing a spinning solution in an inorganic solvent of an acrylonitrile polymer of the following composition by weight, at least acrylonitrile, 010% of another ethylenical- 1y unsaturated compound, and 5% to 15% of a substituted acrylamide of the formula R1 Rs wherein R is selected from hydrogen and methyl and R and R are individually selected from alkyl of 1 to 4 carbon atoms; (2) spinning said polymer solution into an aqueous coagulant; (3) water washing the spun fiber; (4) thermostretching the washed fiber; (5) drying the thermostretched fiber; and (6) heat treating the dried fiber. In a preferred embodiment, the fiber subsequent to water washing and prior to thermostretching is treated with acetone.

The process of the present invention provides noncircular cross section in acrylic fibers that may variously be contoured as elliptical, dog bone shape, cocoon shape, heart shape, or bean shape. Furthermore, the fiber surface is so smooth as to provide exceptional brilliance, thus adding values of considerable merit. In the preferred embodiment, the cross sectional shape will become more noncircular and such forms as cruciform, Y-shapes, or mushroom shapes will emerge. At the same time, the brilliance will be augmented and a distinctive hand characteristic will be imparted to knitted or woven fabrics obtained from such fibers.

It is a remarkable feature of the invention that spinnerettes having noncircular delivery orifices do not have to be employed to obtain the brilliant fibers of noncircular cross section. Accordingly, the restrictions as to the range of spinning conditions associated with the effective use of spinnerettes of noncircular delivery orifices are not applicable to the present process.

In order to obtain brilliant fibers of noncircular cross section, the shape of the delivery orifices used in wet spinning the polymer solution is not critical in accordance with the present invention. Thus, one may use round delivery orifices or such other shaped delivery orifices as may be desired. Although it is generally preferred to employ round delivery orifices so as to avoid the additional expense and difficulties associated with fabricating spinnerettes with noncircular delivery orifices, the present invention leads to fibers of noncircular cross section irrespective of the shape of the delivery orifices. In those instances where noncircular delivery orifices are employed, as previously pointed out, the restrictions as to spinning conditions normally associated with noncircular delivery orifices are not applicable.

It is not known how the present process leads to brilliant fibers of noncircular cross section and it is not necessary that any specific theoretical explanation be given. Surprisingly, however, brilliant acrylic fibers of noncircular cross section result.

In carrying out the process of the present invention, the acrylonitrile polymer employed must have a content of at least 85%, by weight, of acrylonitrile, based on the total weight of polymer. The specified acrylamide comonomer must be present in the range of 5% to same basis. Use of another ethylenically unsaturated compound is optional and may be present up to 10%, same basis. When the specified acrylamide comonomer content is below the range specified, neither the desired brilliance nor noncircular cross section can be achieved in the fiber spun. When the specified acrylamide comonomer content is above the range specified, the physical properties of the fiber are reduced below desirable levels. Effective polymers are binary copolymers consisting of acrylonitrile and a specified acrylamide comonomer and multi-component copolymers consisting of acrylonitrile, one or more specified acrylamide monomers, and one or more ethylenically unsaturated compounds. In binary copolymers are those multi-component copolymers wherein acrylonitrile and several specified acrylamide comonomers are present, the total content of specified acrylamide comonomer is preferably in the range of 9% to c 13%, by weight, based on the total weight of copolymer. In other multi-component copolymers, the content of specified acrylamide comonomer is preferably in the range of 6% to 10%, same basis.

The suitable substituted acrylamides that may be employed include N,N-dimethylacrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-propylacrylamide, N-methylN-butylacrylamide, N,N-dimethylmethacrylamide, N-rnethyl-N-ethylmethacrylamide, N-methyl-N-propylmethacrylamide, N-methyl-N-butylmethacrylamide, N,N-diethylacrylamide, N-ethyl-N-propylacrylamide, N-ethyl-N-butylacrylamide, N,N-diethylmethacrylamide, N-ethyl-N-propylmethacrylamide, N-ethyl-N-butylmethacrylamide, N,N-dipropylacrylamide, N-propyl-N-butylacrylamide, N,N-dipropylmethacrylamide, N-propyl-N-butylmethacrylamide, N,N-dibutylacrylamide, and N,N-dibutylmethacrylamide.

Particularly preferred are the substituted acrylamides and methacrylarnides wherein the two alkyl substituents on the amide nitrogen are the same.

Suitable ethylenically unsaturated compounds include acrylic esters such as methyl, ethyl, butyl, octyl, methoxyethyl, phenyl, and cyclohexyl acrylates; methacrylic esters such as methyl, ethyl, butyl, octyl, methoxyethyl, phenyl, and cyclohexyl methacrylates; unsaturated ketones such as methylvinyl, phenylvinyl, and methylisopropenyl ketones; vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; vinyl ethers such as methylvinyl ether and ethylvinyl ether; styrene and alkyl derivatives thereof; alkyl alcohol and esters and ethers thereof; vinyl and vinylidene halides such as vinyl chloride, vinyl bromide, and vinylidene chloride; and methacrylonitrile.

The useful acrylonitrile polymers may be prepared by any conventional process such as emulsion, solution, or suspension polymerization. As polymerization initiators, those well known in the art may be used including, for example, azobisbutyronitrile, benzoyl peroxide, potassium persulfate, and redox systems such as the combination of sodium chlorate and sodium sulfite. Initiation may also be by conventional means such as by use of light or radioactive rays. Polymerization may be by batch or continuous process or a combination of both.

As polymer solvent, there may be used a concentrated aqueous solution of such inorganic compounds as sodium thiocyanate, potassium thiocyanate, calcium thiocyanate, ammonium thiocyanate, zinc chloride, calcium chloride, nitric acid, and sulfuric acid. Preferred inorganic compounds are the thiocyanates and chlorides mentioned. The inorganic solvent generally contains more than 30% of inorganic compound, preferably more than 40% by weight based on the total weight of water and inorganic compound. The amount of polymer dissolved in the solvent is generally between 3% and 30%, preferably 5% and 20%, by weight, based on the total weight of spinning solution.

The spinning solution prepared as described above, is spun through a spinnerette having suitable delivery orifices into a conventional coagulant, generally a dilute aqueous solution of the inorganic polymer solvent. The filaments obtained are then subjected to additional processing steps as are conventionally employed, including water washing, thermostretching, drying, and heat treating to produce acrylic fibers having noncircular crosssection and spectacular brilliance.

In a preferred embodiment of the invention, the filament, spun as described above, is treated with acetone after water washing and before thermostretching. The treatment is carried out by dipping the fiber into the acetone treating liquor. Although acetone may be used per se, it is generally preferred to employ an aqueous solution of acetone, one containing generally in excess of 10% acetone, by weight, based on the total weight of solution.

The invention is more fully illustrated by the examples which follow, in which all parts and percentages are by weight unless otherwise specifically designated.

EXAMPLE 1 Into a glass vessel mounted in a thermostatic bath maintained at 40 C. and fitted with a thermometer and condenser, were added 13 parts of a monomer mixture consisting of 89% acrylonitrile and 11% N,N-dimethylacrylamide and 87 parts of a 47% aqueous solution of sodium thiocyanate as inorganic solvent. Thioglycolic acid, 0.5% and benzaldehyde, 0.2%, were added as photosensitizers, the percentages being based on the weight of monomers. The polymerization vessel was mounted 5 centimeters from 2 high voltage mercury lamps of 2 kw. size which irradiated the monomer mixture for 2 hours to effect polymerization. Polymer yield was 82.4% and the polymer solution had a viscosity of 6600 centipoises at 30 C. The resulting polymer had a molecular weight of 63,000. The concentration of polymer in the solution was 11.1% and the polymer composition was 89% acrylonitrile and 11% N,N-dimethylacrylamide.

The polymer solution thus obtained was employed as a spinning solution, which was spun into 12% aqueous sodium thiocyanate at 3 C. through a spinnerette having circular delivery orifices, each of a diameter of 0.09 millimeter. The filaments obtained were water washed, thermostretched in boiling water at a stretch ratio of 10, dried at 115 C. for 15 minutes, and heat treated at C. in an atmosphere of steam for 15 minutes. The fiber obtained was of 3.63 deniers and had a tensile strength of 3.28 grams per denier, a knot strength of 2.96 grams per denier, and a tensile elongation of 64.3%. (These properties are typical of conventional acrylic fibers.) The fiber was of cocoon or heart shaped crosssection, had extremely smooth surface, and was of spectacular brilliance.

By contrast, when the above-described example was repeated in every material detail except that methyl acrylate was substituted for N,N-dimethylacrylamide, the fiber was of circular cross section and low brilliance. Similarly, when acrylamide was substituted for N,N-dimethylacrylamide, the fiber was of an irregular and disordered nonconventional procedures lead to fibers of round cross section.

TABLE I.PROPERTIES OF VARIOUS ACRYLIC FIBERS Monomer eomposition* Polymer composition* Fiber properties (percent) Polymer (percent) yield Cross-sectional Example No. AN DMAAm MA (percent) AN DMAAm MA noncireularity Brilliance Gomparative. 90 2 8 75. 3 89. 9 1.8 8. 3 Poor Poor.

90 G 4 70.0 89. 3 6. 4 4. 3 Good Excellent.

90 8 2 69. 89.8 7. 7 2 Excellent Do.

*AN =Acrylonitrile; DMAAm N, N dimethylacrylamide; MA =Methyl acrylate.

EXAMPLE 2 An inorganic solvent solution of a polymer containing 88.6% acrylonitrile and 11.6% N,N-diethylacrylamide was prepared following the procedure of Example 1 in every essential detail except that the temperature 01 polymerization was 50 C. The polymer obtained had a molecular weight of 83,700.

The polymer solution thus obtained was spun under the conditions described in Example 1. There was obtained a fiber of desired non-circular cross-section and high brilliance.

In an additional run, the fiber subsequent to water washing and prior to thermostretching was passed through a 50% aqueous acetone solution. The fiber obtained was of greater noncircularity with respect to cross section and had a more spectucular brilliance when the acetone treatment was omitted.

EXAMPLES 3 AND 4 Additional spinning solutions were prepared following the procedure of Example 1. These solutions were indi- 'vidually spun following the procedure of Example 1. The various polymer compositions employed and fiber properties are given in Table I.

The results of Table I show that a ternary polymer containing in excess of 5% N,N-dimethylacrylamide provides fiber having desirable noncircular cross section and excellent brilliance.

EXAMPLE 5 The procedure of Example 1 was followed in all essential details with the exception that the delivery orifices were square shaped with each side of the square being 0.07975 millimeter. In this example, as in Example 1, the take-up ratio of the coagulated fiber to the average extrusion velocity of the spinning solution through orifices is 1.0.

The fibers obtained have essentially the same crosssectional shape and properties as those obtained in Example 1. This example shows that fibers of noncircular cross section are obtained when noncircular delivery orifices are employed under spinning conditions which in conventional procedures lead to fibers of round cross section.

EXAMPLE 6 The procedure of Example 1 is again followed in all essential details except that the delivery orifices are of elliptical shape with the major radius being 0.006364 millimeter and the minor radius being 0.003182 millimeter. In this example, as in Example 1, the take-up ratio of the coagulated fiber was equal to the average extrusion velocity of the spinning solution through the orifices.

The fibers obtained have essentially the same crosssectional shape and properties as those obtained in Example 1. This example also shows that fibers of noncircular cross section are obtained when noncircular delivery orifices are employed under spinning conditions which in We claim:

1. A process for producing brilliant acrylic fibers of noncircular cross section which comprises: (1) preparing a spinning solution in an inorganic solvent of an acrylonitrile polymer of the following composition by weight, at least acrylonitrile, 010% of another ethylenically unsaturated compound, and 5% to 15% of a substituted acrylamide of the formula wherein R is selected from hydrogen and methyl and R and R are individually selected from alkyl of 1 to 4 carbon atoms; (2) spinning said polymer solution through a spinnerette having delivery orifices into an aqueous coagulant; (3) water-washing the coagulated fiber; (4) thermostretching the washed fiber; (5) drying the thermostretched fiber; and (6) heat treating the dried fiber.

2. The process of claim 1 wherein said substituted acrylamide contains the same alkyl group as substituents R2 and R3.

3. The process of claim 1 wherein said polymer is a binary copolymer.

4. The process of claim 1 wherein said polymer is a ternary copolymer.

5. The process of claim 3 wherein the amount of said substituted acrylamide present in said polymer is 9% to 13% by weight.

6. The process of claim 4 wherein the amount of said substituted acrylamide present in said polymer is 6% to 10% by weight.

7. The process of claim 1 wherein subsequent to water washing and prior to thermostretching said fiber is treated with acetone.

8. The process of claim 1 wherein said polymer composition by weight is 89% acrylonitrile and 11% N,N-dimethylacrylamide.

9. The process of claim 1 wherein said polymer composition by weight is 88.6;% acrylonitrile and 11.4% N,N- diethylacrylamide.

10. The process of claim 9 wherein subsequent to water washing and prior to thermostretching said fiber is treated with acetone.

11. The process of claim 1 wherein said polymer solution is spun through a spinnerette having round delivery orifices.

12. The process of claim 1 wherein said polymer solution is spun through a spinnerette having noncircular delivery orifices.

(References on following page) References Cited UNITED STATES PATENTS Coover et a1. 260-296 AN Fujisaki et a1 264-182 Menault 8-1301 Fujisaki et a1. 264-182 Fujisaki et all 260-296 AN Reader 260-296 AN Dagon et a1. 264-182 Fitzgerald et a1 264-182 Buysch et a1. 260-296 AN Shimamura et a1. 264-177 F JAY H. WOO, Primary Examiner US. Cl. X.R. 

